Pleomorphism and Growth Cycles in Trichophyton mentagrophytes

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Abstract
The growth cycles of three strains of the dermatophyte Trichophyton mentagrophytes have been investigated. The 3 strains studied were a conidial form (N) and 2 pleomorphic variants obtained from aged N_cultures. The 2 variants were an intermediate form (6-1) and a highly pleomorphic type (HI). On a neopeptone-dextrose medium the rate of growth, final dry weight, and length of the growth phase were significantly greater in 2 variant strains. On a casein-hydrolysate-dextrose medium a different growth pattern was manifested. All 3 strains grow at the same rate for the first 3 days, but then all suffer a sharp diminution in growth rate. The severity of the drop is also correlated with the degree of pleomorphism, the drop being greatest in the N_and least in the HI cultures. The growth period (6 days) is the same for the 3 strains so that differences in final dry weight are due to the differential growth rates in the 2nd growth phase (3rd to 6th day). In addition to this 2-phase growth cycle with no interposed lag period, a type of growth cycle superficially resembling diauxie was manifested by the N_form. This phase corresponds temporally with the morphological manifestation of the pleomorphic variants within the conidial colony.